RDMA/qedr: Fix KASAN: use-after-free in ucma_event_handler+0x532

Private data passed to iwarp_cm_handler is copied for connection request /
response, but ignored otherwise.  If junk is passed, it is stored in the
event and used later in the event processing.

The driver passes an old junk pointer during connection close which leads
to a use-after-free on event processing.  Set private data to NULL for
events that don 't have private data.

  BUG: KASAN: use-after-free in ucma_event_handler+0x532/0x560 [rdma_ucm]
  kernel: Read of size 4 at addr ffff8886caa71200 by task kworker/u128:1/5250
  kernel:
  kernel: Workqueue: iw_cm_wq cm_work_handler [iw_cm]
  kernel: Call Trace:
  kernel: dump_stack+0x8c/0xc0
  kernel: print_address_description.constprop.0+0x1b/0x210
  kernel: ? ucma_event_handler+0x532/0x560 [rdma_ucm]
  kernel: ? ucma_event_handler+0x532/0x560 [rdma_ucm]
  kernel: __kasan_report.cold+0x1a/0x33
  kernel: ? ucma_event_handler+0x532/0x560 [rdma_ucm]
  kernel: kasan_report+0xe/0x20
  kernel: check_memory_region+0x130/0x1a0
  kernel: memcpy+0x20/0x50
  kernel: ucma_event_handler+0x532/0x560 [rdma_ucm]
  kernel: ? __rpc_execute+0x608/0x620 [sunrpc]
  kernel: cma_iw_handler+0x212/0x330 [rdma_cm]
  kernel: ? iw_conn_req_handler+0x6e0/0x6e0 [rdma_cm]
  kernel: ? enqueue_timer+0x86/0x140
  kernel: ? _raw_write_lock_irq+0xd0/0xd0
  kernel: cm_work_handler+0xd3d/0x1070 [iw_cm]

Fixes: e411e058

 ("RDMA/qedr: Add iWARP connection management functions")
Link: https://lore.kernel.org/r/20200616093408.17827-1-michal.kalderon@marvell.com
Signed-off-by: Ariel Elior <ariel.elior@marvell.com>
Signed-off-by: Michal Kalderon <michal.kalderon@marvell.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>